ref: 905e669fced93d8f1648157ade1456227230b979
dir: /man/2/arrays/
.TH Arrays 2
.SH NAME
arrays: find, append, prepend, tail, pair, filter, map\- array operations
.SH SYNOPSIS
.EX
include "arrays.m"
arrays := load Arrays Arrays->PATH;
find: fn[T](a: array of T, x: T): array of T
for { T => Equals: fn(a, b: T): int; };
append: fn[T](a₀: array of T, x: T): array of T;
prepend: fn[T](a₀: array of T, x: T): array of T;
tail: fn[T](a: array of T): array of T;
pair: fn[T₁, T₂](a₁: array of T₁, a₂: array of T₂): array of (T₁, T₂);
stringify: fn[T](a: array of T): string
for { T => String: fn(a: self T): string; };
filter: fn[T](a: array of T, f: ref fn(x: T): int): array of T;
map: fn[T](a₀: array of T, f: ref fn(x: T): T): array of T;
.EE
.SH DESCRIPTION
The module
.I arrays
provides operations on arrays of type
.IR T ,
which may be any reference type, or
.BR string .
Reference types are
.BR array ,
.BR chan ,
.BR array ,
.BR module ,
and
.BI ref " adt".
None of the operations change their parameter arrays: they always return a new array.
.PP
First, there is a group of common array operations.
.PP
.B Find
finds the first instance of
.I x
in array
.I a
and returns the slice
.IR a[x:] .
.B Find
returns nil if there is no
instance of
.I x
in
.IR a .
The type
.I T
must implement a method
.I Equals
which returns a number greater than zero if the elements
.I a
and
.I b
are equal and zero if
.I a
and
.I b
are not equal.
.PP
.B Append
returns a new array with the elements of
.I a₀
followed by the element
.IR x .
.PP
.B Prepend
returns a new array with the element
.I x
followed by the elements of
.IR a₀ .
.PP
.B Tail
returns a new array which is the slice
.IR a[1:] .
Nil is returned if the length of a is less than 2 elements.
.PP
.B Pair
takes two arrays
.I a₁
and
.IR a₂ ,
and returns a new array of tuples
.BI ( v1,\ v2 )
in which each element of
.I a₁
has been paired with the corresponding element of
.IR a₂ .
Nil is returned if the arrays are not equal in length.
.PP
.B Stringify
returns a visually pleasing string representation of
.IR a .
The type
.I T
must implement a method
.I String
which returns a string representation of an element in the array of type
.IR T .
.PP
A second group of operations applies a function
.I f
or a Boolean predicate
.I p
to each element of a array, returning a transformed array or a Boolean value.
A predicate
.I p
must return non-zero if its parameter value satisfies its condition, and must return zero if it does not.
.PP
.B Filter
returns a new array containing only the elements of
.I a
that satisfy
.IR p .
.PP
.B Map
returns a new array in which each element of
.I a₀
has been transformed by
.I f
(ie, if
.I a₀
is
.IB e0, e1, ⋯
then the result is
.IB f(e0), f(e1), ⋯ ).
.SH SOURCE
.B /appl/lib/arrays.b
.SH BUGS
The current implementation of polymorphism is limited to reference types and strings,
which in turn limits use of this module.
.SH SEE ALSO
.IR lists (2)